something i have been playing with this last week
vactrol type isnt fussy i am using NSL32 but could just as well be
vtl5c3, A slow closing vactrol like a vtl5c4 could be interesting also
the P2 connector goes to a B100k pot pin 2 is the wiper just reverse 1 and 3 if left / right is wrong way round . note with the pot in the centre and no cv input there is no output.or at least very little
CV input can be from an LFO output +5 to -5 volts though going to the rails will not hurt anything.
T1 and T2 adjust the sensitivity for the vactrols you can get them pretty good just by watching the panel leds PD-L / PD-R while adjusting P2 for the supplied voltage though the actual vactrol response is slightly different to normal leds so also use your ears
anyway hope someone can use this
edit: 09/11/12 see post further down this page for latest rev

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as good an answer as anyLast edited by diablojoy on Fri Nov 09, 2012 12:18 am; edited 1 time in total

Hmm must remenber to post the schematic for this
No dont think i have seen that one, though it probably couldn't be that much different .
the idea for the basic vactrol drive circuitry initially came from when i was looking at Scott stites mutant filter though obviously i added quite a bit to that
this is the cct i used for my Blacet Time machine build where in that case i actually wanted silence when the pan pot was centered and when no cv is being applied as it was for the wet signal only.
i also added a gated inverter to the CV in on that build so i could use a cv from a sequencer and a clock output into the gate input to get the necessary negative excursions.
I was thinking of revisiting this one at some point to see if i can change the manual pan response using a dual gang pot instead for the case when you actually want an output with the pot centered though there is always going to be some compromise doing that because it is a vactrol cct.

Im not sure where Mark took this from (maybe he made it up) but there's tons of vactrol panniers and faders in the Buchla 200 schematics obviously. There are two panners on the 206 dual mixer, and a fader in the 240 freq shifter/balanced mod.

diablojoy wrote:

Quote:

Is this for the schematic on Mark Verbos' site?

Hmm must remenber to post the schematic for this
No dont think i have seen that one, though it probably couldn't be that much different .
the idea for the basic vactrol drive circuitry initially came from when i was looking at Scott stites mutant filter though obviously i added quite a bit to that
this is the cct i used for my Blacet Time machine build where in that case i actually wanted silence when the pan pot was centered and when no cv is being applied as it was for the wet signal only.
i also added a gated inverter to the CV in on that build so i could use a cv from a sequencer and a clock output into the gate input to get the necessary negative excursions.
I was thinking of revisiting this one at some point to see if i can change the manual pan response using a dual gang pot instead for the case when you actually want an output with the pot centered though there is always going to be some compromise doing that because it is a vactrol cct.

I remember when Verbos' vactrol panner and fader were discussed before in these forums, a lot of people mentioned that they had difficulty getting them to work. For this reason, I never experimented with them much-- but I now have a need for some compact panner and fader circuits and so it's probably time to re-visit these vactrol circuits.

slight changes plus scheme
edit : deleted bad attachments_________________In an infinite universe one might very well
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as good an answer as anyLast edited by diablojoy on Mon Nov 05, 2012 12:07 am; edited 1 time in total

I've etched and built one of these but unfortunately the right channel doesn't work. While debugging I noticed some inconsistencies and an error on the PCB:

- The schematic uses 2N3904 throughout, but the board overlay specifies two 2N3904 and two 2N3906 transistors
- One 1M resistor is connected to the anode of the right Vactrol instead of +15V
- The 47K resistors going to GND in the pan pot voltage dividers are not connected to the pot lugs but to the positive and negative rails.

Did you ever build it using this layout, diablojoy? If yes, how does it need to be modified to work?

oh dear sorry to hear that .
it has been a long time since i did this, i will have to go over it tonight and get back to you .
there were 3 or 4 original prototypes but I definitely have a working version_________________In an infinite universe one might very well
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dammit
the layout i posted was the wrong one [a failed version ]
for the very reasons you point out
I thought i had got rid of it of my drive edit : i was having a very bad day it seems i deleted the good one , will endevour to ressurect it.
really sorry for that.
I also found something else in the scheme that needs attention
there are also 2 summing resistors and diodes missing for P2
not something that would actually prevent it working, just bad
so i will need to fix that on the scheme and repost the correct versions
and yes it should be 2 x 2n3904 and 2 x 2n3906._________________In an infinite universe one might very well
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OK sorry roglok for the wait i had to redo this as i couldnt recover the original correct files
however not too bad the layout is basically as close to the one i had working as i can get. I etched and built it to make double sure anyway
so yes this one definitely works.
must get more vactrols
I think slow ones would be best with this.
but panning bouncy stuff is cool as well
cv source = +/-5v LFO signal is good

_________________In an infinite universe one might very well
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as good an answer as anyLast edited by diablojoy on Thu Nov 08, 2012 11:47 pm; edited 1 time in total

However, before I start modding my board:
PCB and schematic are different again... In the current overlay, the Vactrol LED cathodes are connected to the panel LED cathodes. In the scheme the Vactrol LED is flipped...

I believe the parts overlay is correct
as i actually glued a printed version directly on the board before stuffing
to work from and it is working fine.
At the moment i print them directly from the pdf and use board laquer
to attach them [ must be printed on bubblejet with that way ] though just PVA glue would probably work as well [must try that soon ] or you could probably just use a self adhesive paper. drill the board first before attaching and then just use a sharp scriber to punch through the paper once its set definitely makes stuffing self etched boards easier and quicker.

Quote:

In the current overlay, the Vactrol LED cathodes are connected to the panel LED cathodes. In the scheme the Vactrol LED is flipped...

yep i didnt flip the orientations as i should have in the scheme will sort tonight
the panel LED's should be run in series with the vactrols and need to be installed for the unit to work with all anodes toward the +V behind the 470R resistors, hmm i should swap the connectors 180 degrees for the the panel LED's on the board as well too, those square pads are misleading

Quote:

Thanks and sorry for bugging you!

Haha no bugging just glad someone's taken some interest. Besides you found many issues that i otherwise would not have realised exsisted
so i get to learn as well._________________In an infinite universe one might very well
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OK sorted finally i hope
dont know what drugs i was on but the scheme wasn't even close to being correct, luckily i didnt go off that when i redrew the board, i followed closely the traces of the existing original board.
anyway the scheme should now make a whole lot more sense.
also I flipped the panel LED connectors on the board so they are now less confusing, especially if installing LED's directly
cathodes are to square pads
that is the only change for the actual foil and component overlay_________________In an infinite universe one might very well
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just do this circuit but one channel doesn't work really,
one LED blink but the other one stay bright all the time,

What CV are you inputting - this circuit expects a bipolar CV
eg the output from an LFO +/-5V a sine wave or triangle is best to start with
also the manual pot should be centered at 12 oclock otherwise it will skew the pan right or left depending on its position_________________In an infinite universe one might very well
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look for DC level shifter under HOT TIPS
Gain will need to equal 1 - use the fixed gain - RIN= RFB so same value
adjust offset voltage to get what you need - simple_________________In an infinite universe one might very well
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